Slot antenna utilizing variable standing wave pattern for controlling slot excitation



June 27, 1967 J. A. ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLINGSLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 1 1 i7 1 L i 2 L 3 2L I JL 46B ,Z/ L L 32 2/8 FIG.2 25 5 ,w/I

INVENTOR.

JERRY A. ALGEO i BY SIDNEY MAGNES AGENT June 2 7, 1967 J. A. ALGEO3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLINGSLOT EXCITATION Filed March 12, 1964 5 SheetsSheet 2 so x 62 I- I 66A IL 5 &

83 v JL I 706 j sec sec 70 INVENTOR. JERRY A. ALGEO SIDNEY MAGNES AGENTno 0 t 00 m 8 2 6 w 3% m s 5 June 27, 1967 J. A. ALGEO SLOT ANTENNAUTILIZING VARIABLE STANDING WA PATTERN FOR CONTROLLING SLOT EXCITATIONFiled March 12, 1964 INVENTOR JERRY A ALGEO SIDNEY MAGNES AGENT...

June 27, 1967 J. A. ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLINGSLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 4 JERRY A. ALGEOSIDNEY MAGNES AGENT June 27, 1967 J ALGEO 3,328,800

SLOT ANTENNA UTILIZING VARIABLE STANDING WAVE PATTERN FOR CONTROLLINGSLOT EXCITATION Filed March 12, 1964 5 Sheets-Sheet 5 FIG. l3

INVENTOR JERRY A. ALGEO FIG SIDNEY MAGNES AGENT.

United States Patent SLOT ANTENNA UTILIZING VARIABLE STAND- lNG WAVEPATTERN FOR CONTROLLING SLOT EXCITATION Jerry A. Algeo, Buena Park,Calif., assignor to North American Aviation, Inc. Filed Mar. 12, 1964,Ser. No. 351,320 9 Claims. (Cl. 343-768) This invention relates toantennas; and more particularly to antennas that can produce differentradiation and reception patterns, and different types ofenergy-polarization.

It is well known that radar operates upon the echo principle. Inoperation, a radar station causes its antenna to transmit energyoutwardly to impinge upon a target; the target reflecting some of theimpinging energy in the form of a return, or echo, signal. The antennareceives the reflected echo signal; and equipment in the radar stationprocesses the reflected energy to provide target information, such asthe direction of, and distance to, the target.

The distance to the target is obtained by measuring the length of timethat elapses between the transmission of the radar energy and thereception of the echo signal, the direction of the target beingobtained-depending upon the radar system-from the echo signal or thedirection in which the antenna is aimed.

As is well understood in the art, radar energy has the characteristicthat it may be polarized, the energy may be linearly-polarized eithervertically, horizontally, or at any intermediate angle; or it may bepolarized elliptically, of which circular polarization is a specialcase.

The polarization of the radar energy enters into the operation of theradar system in the following manner.

Assume that an airplanes radar operator is interested -for navigationalpurposes-in knowing whether the plane is flying over water, desert, ormountainous terrain. It has been found that circularly-polarized radarenergy causes the magnitude of the echo signal to vary With changes interrain; and, in this case, the radar operator would therefore prefer touse circularly-polarized radar energy. If, however, he is primarilyinterested in the planes height above the ground, he would prefer to uselinearly vertically-polarized radar energy, since this produces echosignals of substantially the same magnitude regardless of the type ofterrain.

It has also been found that in a rain storm the echo signal depends onthe size and shape of the raindrops of the storm. Therefore, if theradar operator is trying to obtain information about the location andextent of a rain storm, it is desirable to select the type ofpolarization that provides the strongest return echo signal from theraindrops themselves. If, on the other hand, the radar operator isinterested in a target beyond the rain storm, it is desirable to selectthe type of polarization that pierces the rain storm, and is reflectedby targets beyond the storm.

Thus, it is desirable to be able to change the polarization of the radarenergy.

The type of polarization may be unimportant under other conditions, suchas searching for, and tracking a target; but-under these conditions-anitem of great importance is the radiation-pattern, that is, the amountof radar energy that is radiated in various directions.

For example, in the searching mode of operation, when the radar operatoris trying to detect a target, the radiation-pattern is preferably a widebeam, so that any target within the beamwidth will produce an echosignal. Once the presence of a target within the beamwidth has beenindicated, the radar operation is changed to a so- 3,328,800 PatentedJune 27, 1967 called tracking mode, wherein the radiation-pattern ischanged to a narrow pencil-like beam that isused to pinpoint thedirection of the target.

Other modes of radar operation require still different types ofradiation-patterns.

It will be understood from the above discussion, that it is desirable tobe able to change both the polarization and the radiation-pattern,depending upon particular op erating conditions.

It is therefore the principal object of the present invention to providean improved antenna having means for providing selected combinations ofpolarization and radiation pattern.

The attainment of this object and others will be realized from thefollowing specification, taken in conjunction with the drawings ofwhich:

FIGURES 1, 2, 3, and 4 illustrate antennas for producing different typesof radar-energy polarization;

FIGURES 6 and 9 illustrate different beam patterns;

FIGURES 5, 7, 8, 10, and 11 illustrate antennas for producing differentbeam patterns; and

FIGURES l2 and 13 illustrate antennas having different cross-sectionalshapes.

Broadly speaking, the present invention contemplates an antenna in whichthere is established a standing-wave pattern of radar energy. Bypermitting the energy to escape from the antenna only at selected pointstherealong, the emergent energy has a given beamwidth which is polarizedin a given manner. By permitting the energy to escape from the antennaonly at other selected points, the emergent energy may have a diiferen-tbeamwidth which is polarized in a different manner. Thus, by controllingthe points from which the energy escapes, the combination of beamwidthand polarization of the energy can be selectively controlled.

Alternatively, the amounts of different types of polarization can beselectively combined, so that the emergent energy is polarized in stillanother manner.

The present invention contemplates control of the polarization by (1)establishing a standing-wave pattern that permits the energy to escapefrom given points, and thus provides emergent energy of a givenpolarization; and then (2) changing the standing-Wave pattern to onethat permits the energy to escape from different points, and thusprovides emergent energy of a different polarization.

In this way the instantaneous controlled standing-Wave patternestablishes the polarization of the radar energy.

The present invention also contemplates the production of particularradiation-patterns by establishing standingwave patterns that cause theenergy to escape from given sets of points, the arrangement of theescape-points establishing the radiation-pattern or beamwidth.

Moreover, the present invention also contemplates a constantly-changingstanding-wave pattern, so that the energy emerges in aconstantly-changing combination of polarization and radiation pattern.

FIGURE 1 shows an antenna that radiates linearlypolarized energy. Theantenna 20 comprises a hollow tubular waveguide 22, made of anelectrically-conductive material such as copper or the like. Waveguidessuch as element 22 are ordinarily used to guide microwave energy fromone point to another, hence their name waveguide. However, if thewaveguide has an aperture (or slot) in the wall thereof, energy willtend to escape through the aperture. Moreover, if the waveguide has anarray of slots or a set of intentionally-introduced apertures that aresuitably sized, shaped, spaced, oriented, etc., the energy escaping fromthe various apertures will com bine to form a specificradiation-pattern; and the waveguide then acts as a radiating, ortransmitting antenna. This will be more fully discussed hereinafter.

In FIGURE 1, antenna 20 comprises an aperturedwaveguide 22 having ashorting plate 24 of electricallyconductive material positioned at oneend of waveguide 22. shorting-plate 24 physically and electricallycloses the end of the antenna. It therefore produces an electricalshort-circuit; and energy cannot escape from the closed end of theantenna 20.

shorting-plate 24 has the characteristic that when energy is applied tothe open bottom-end of the antenna as in icated by arrow 25-theshorting-plate 24 reflects the energy in such a way that a voltagestanding-wave" pattern is produced; the voltage standing-wave beingrepresented by sinusoidal waveform 26.

It will be noted that sinusoidal waveform 26 has a positive maximumvalue at certain cross-sectional planes such as 28; that sinusoidalwaveform 26 has negative maximum values at other cross-sectional planessuch as 30; and that sinusoidal waveform 26 has an intermediate value ofzero at other cross-sectional planes, such as 32.

The sinusoidal waveform 26 has a characteristic known as its wavelength,which extends between corresponding pointsfor example, from a zero valuethrough a negative maximum value and a positive maximum value back to azero value. A wavelength of waveform 26 is represented by the distanceL.

It has been found that if a transverse slot-like aperture 34A is cutthrough the broad wall of the waveguide 22 at a cross-sectional plane 32where the sinusoidal waveform 26 has a value of zero, then thestanding-wave will be coupled to the aperture; and energy will escapethrough the aperture. The emergent energy will be polarized in a linearlongitudinal manner as indicated by the arrow 38A, which has alongitudinal orientation.

If another transverse slot 34B is similarly positioned at a zero-valuedplane 32 that is one wavelength from the first slot 34A, it too willpermit the escape of energy; the energy from transverse slot 34B alsobeing polarized in the same linear longitudinal manner, as shown byarrow 38A.

Thus, a group of transverse slots 34A, 34B, etc. that are similarlypositioned one-wavelength apart-or multiples of one-Wavelengthapart-will permit the escape of energy that is similarly-polarized in alinear longitudinal manner.

If another transverse slot 34C is positioned at a zerovalued plane 32that is spaced one-half wavelength from the first slot, or is spacedone-half wavelength from a transverse slot of the first set, it too willpermit the escape of energy. If the slot 34C is positioned on the otherside of the longitudinal axis of the antennas broad wall, the energyescaping from slot 34B will have the same linear longitudinalpolarization, as shown by arrow 38C.

Thus a second group of transverse slots 34C, 34D, etc., spaced onewavelength apart, half-a-wavelength from the slots of the first group,and staggered with respect to the slots of the first group, will permitthe escape of energy that is similarly-polarized in a linearlongitudinal manner.

In this way, a set of staggered transverse slots positioned one-halfwavelength apart at the zero-valued points of the standing-wave pattern26 converts the waveguide to an antenna; and the energy emerging fromthe above set of slots combines to form a radiation-pattern of linearlongitudinal polarization; the radiation pattern itself to be discussedlater.

If the antenna is positioned vertically, as shown in FIGURE 1, theenergy emerging from the set of transverse slots will be linearlypolarized vertically, as shown by the vertical arrows 38; whereas, ifthe antenna were positioned horizontally, the emergent energy would belinearly horizontally-polarizedthat is, arrows 38 would then behorizontal.

It should be noted that in order to produce the abovedescribedlongitudinal polarization of the emergent energy, the shorting-plate 24must be spaced from the first slot 34A by a distance that is equal toone-half a wavelength; or by a distance that is equal to an integralnumber of half-wavelengths. This spatial relation is necessary in orderto place all of the lots simultaneously at the zerovalued points of thevoltage standing-wave pattern 26.

While FIGURE 1 shows shorting-plate 24 positioned at the end of theantenna, and one-half wavelength from the first slot, the shorting platecould just as well have been positioned at any of the zero-valued crosssectional planes 32 in accordance with the above explanation; althoughthis arrangement would dis-able the apertures on the side of theshorting-plate away from the entrypoint of the energy (arrow 25).

FIGURE 2 shows a similar antenna 40 that comprises an aperturedrectangular waveguide 42 and a shortingplate 24 that produces astanding-wave indicated by sinusoidal waveform 26. It has been foundthat if a longitudinal slot-like aperture 46A is cut through the broadwall of the waveguide 42 at a cross-sectional plane 28 where thesinusoidal waveform 26 has a maximum positive value, then thestanding-wave will be coupled to the aperture; and energy will escapethrough the aperture. The emergent energy Will now be polarized in alinear transverse manner as indicated by arrow 48A, which has atransverse orientation.

If another longitudinal slot 46B is similarly positioned at a maximumpositive valued plane 28 that is one wavelength from the first slot 46A,it too will permit the escape of energy; the energy also being polarizedin the same linear transverse manner, as shown by arrow 4813.

Thus, a group of longitudinal slots 46A, 46B, etc., that are similarlypositioned one-wavelength apart--or multiples of one-wavelengthapartwill permit the escape of energy that is similarly-polarized in alinear transverse manner.

If another longitudinal slot 46C is positioned at a maximum-valuedpositive plane 28 that is spaced onehalf wavelength from a longitudinalslot of the first set, it too will permit the escape of energy. Theenergy in this case has the same linear transverse polarization if theslot 46C is positioned on the other side of the longitudinal axis of theantennas broad wall.

Thus, a second group of longitudinal slots 46C, 46D spaced onewavelength apart, half a wavelength from the slots of the first group,and staggered with respect to the slots of the first group, will permitthe escape of energy that is similarly-polarized in a linear transversemanner.

In this way. a set of staggered longitudinal slots positioned one-halfwavelength apart at the maximum-valued points of the standing-wavepattern 26, converts the Waveguide to an antenna; and the energyemerging from the set of slots combines to form a radiation-pattern oflinearly transverse polarization; the radiation-pattern itself to bediscussed later.

If the antenna is positioned vertically, as shown in FIGURE 2, theenergy emerging from the set of longitudinal slots will be linearlypolarized horizontally, as shown by the vertical arrows 48; whereas, ifthe antenna were positioned horizontally, the emergent energy would belinearly vertically polarizedthat is, arrows 48 would then be vertical.

It should be noted that in order to produce the abovedescribedtransverse polarization of the emergent energy, the shorting-plate 24must be spaced from the first slot 46A by a distance that is equal to anodd multiple of quarter-wavelengths. This spatial relation is necessaryin order to place all of the slots simultaneously at the maximum-valuedpoints of the voltage standing-wave pattern 26.

To recapitulate, it may be understood that by positioning a set ofsuitably-oriented slots at selected locations relative to astanding-wave pattern, the emergent energy may be selectively polarizedin a desired manner.

The above discussion has shown that it is possible for an antenna toproduce either longitudinally or transversely-polarized emergent energy.FIGURE 3 shows how a single antenna can produce either type ofpolarization.

In FIGURE 3, antenna 60 comprises a waveguide 62, a shorting plate 64,and a first set of staggered longi tudinal slots 66A, 66B, 66C, etc.that are spaced apart a distance of half a wavelength. As previouslyindicated, the set of longitudinal slots can produce emergent energythat is linearly transversely-polarized.

FIGURE 3 also shows a second set of staggered transverse slots 70A, 70B,70C etc., that are on the same cross sectional plane as the longitudinalslots 66; and are therefore also half a wavelength apart. As previouslyindicated, the transverse slots can produce emergent energy that islinearly longitudinally-polarized.

It will be noted that the slots of the two sets are so positioned thatthe slots form slot-pairs 66A, 70A; 66B, 70B; 66C, 70C, etc. comprisingone longitudinal slot 66 and one transverse slot 70 positioned at eachcross-sectional plane; and that the slots-pairs are spaced apart by halfa wavelength.

In FIGURE 3, when energy is introduced at the lower end of the antenna,the shorting-plate 64A establishes a standing-wave pattern 80 havingzero points or nulls positioned at the slot-pairs. Therefore, thetransverse slots 70 would emit longitudinally-polarized energy, asexplained in connection with FIGURE 1.

However, the longitudinal slots 66, also positioned at the zero-valuedpoint of the standing-wave pattern 80, do not permit any energy toescape through them.

Thus, for the location shown for shorting-plate 64A, the emitted energywould be longitudinally-polarized.

If the shorting plate is moved to the location 648, and energy isintroduced at the lower end of the antenna, the dotted-line standingwave pattern 81 will be produced.

It will be seen that the maximum-valued points of the standing-wavepattern 81 are now at longitudinal slots 66, and the escape oftransversely-polarized energy resulting, as explained in connection withFIGURE 2. However, the transverse slots 70 also positioned at themaximum-valved points of standing-wave pattern 81, and therefore theywill not permit any (longitudinally polarized) energy to escape throughthem. Accordingly, for the 64B location of the shorting-plate (in FIGURE3), the emitted energy would be transversely-polarized.

Thus, by inserting or withdrawing a removable shorting-plate at location64B (in FIGURE 3), the emergent energy can be polarized in a transverseor in a longitudinal manner respectively.

It has been found that a maximum amount of energy escapes from the slotif the slot has a periphery that is approximately equal to thewavelength of the energy. In a typical case, the length of the slot isabout onehalf of the wavelength, and the width of the slot is aboutone-twentieth of the wavelength,

It has also been found that progressively-more energy is permitted toescape as the slot is progressively offset from the center line of thebroad wall of the antenna. Thus, by suitably positioning a plurality ofsuitablyshaped slots, the amount of escaping radiation can becontrolled.

It was previously indicated that the amount of energy escaping through aslOt can be controlled by the size of the slot, and by the amount ofoffset from the longitudinal axis of the antenna. If the same mounts ofperpendicularly-polarized energy escapes from the separate slots of aslot-pair, the emergent energy combines to produce socalledcircularly-polarized energy.

In FIGURE 4, antenna 84 produces circularly-polarized energy by using ashorting-plate at the location indicated by reference character 64C, andby using slotpairs that are positioned one wavelength apart. Theshorting-plate at this location, produces a standing-wave patternindicated by the solid sinusoidal line 82.

It will be noted that each slot of the slot pairs is now positioned,relative to the standing-wave pattern 82, at

a point that is neither maximum-valued nor zero-valued. As a result ofthis particular intermediate value, equal amounts of energy escapethrough each slot of each slot pair; thus resulting incircularly-polarized energy.

The circularly-polarized energy has a characteristic known asright-handedness or left-handedness; which is established by thelocation of the slot-pair relative to the standing-wave pattern. InFIGURE 4, for example, each slot-pair is at a location that producespolarization of the same handness.

If the slot-pairs were placed at locations half-way between thoseillustrated, and were offset to the other side of the longitudinal axisof the broad wall of the antenna, they would produce polarization of theopposite handness. This same opposite handness can also be achieved byestablishing a standing-wave pattern such as 83, by the use of ashorting-plate 64D. Thus by using inserta'ble shorting-plates, eitherright-handed or left-handed circularly-polarized energy can be produced.

It has been shown that the standing-wave patterns of FIGURE 4 producecircularly-polarized energy by causin-g equal amounts of energy .toescape from each slot of a slot-pair. If now, the standing-wave patternwere changedas by slightly re-positioning the shorting-plate, moreenergy would escape from one slot than from the other. The resultantemergent energy would no longer be circularly polarized; butwould now'be elliptically polarized.

It is therefore apparent that the antenna of FIGURE 4 maybe made toestablish a standing-wave pattern that produces polarization havingdifierent degrees of ellipticity; each of which may be right-handed orleft-handed.

It is well known that antennas generally act in a reciprocal manner. Forexample, if an antenna transmits only horizontally-polarized radiation,it will receive only horizontally-polarized radiation. Similarly, if anantenna transmits vertically-polarized radiation, it will receive onlyvertically-polarized radiation. In a like manner, if an antennatransmits elliptically'or circularly-polarized radiation, it willreceive only elliptically-or circularly polarized radiation. Moreover,if the antenna transmits right-hande or left-handed-elliptically orcircularly polarized radiation (controlled by the type of slot pairsselected), it will receive only the same type of radiation. Thisconforms to the theory of reciprocity.

The previously-disclosed antennas act in accordance with the theory ofreciprocity; and as a result they have a number of novel uses.

'For example, if right-handed polarized energy is transmitted toward arainstorm, the raindrops reflect the energy; and the echo signalcomprises left-hand polarized energy. Thus, if the radar operator Wantsinformation about the rainstorm, he establishes a standing-wave patternthat causes the antenna to transmit right-handed polarized energy; andhe then changes the standing-wave pattern so that the antenna willreceive the left-handed polarized radiation reflected by the raindrops.The radar system then provides information about the energy-reflectingraindrops.

If, however, the radar operator wants information about targets beyondthe rainstorm, he establishes a standingwave pattern that causes theantenna to transmit righthanded polarized energy; and he maintains thesame standing-wave pattern, so that the antenna receives theright-handed circularly-polarized energy that is reflected by themore-distant targets beyond the rainstorm. Thus, the radar system doesnot receive the echo signals from the raindrops; but does receive theecho signals from the targets.

Moreover, the radar operator can establish a standingwave pattern whoseellipticity is optimum for reflection, or rejection, or the raindropsecho signals.

Pulsed radar systems are also plagued by echo signals known ,as"second-time-around-signals. These echo signals are produced by objectsthat are farther away than the maximum range of interest represented bythe pulse repetition period of the radar; and such echo signals, inresponse to a transmitted energy pulse, arrive at the radar stationduring the subsequent pulsing period, whereby a false target-rangeindication is provided.

The present invention obviates these signals in the following manner.For an initial pulse repetition period, for example, the radar operatorestablishes a standing-wave pattern that causes the antenna to produce,say, horizontally-polarized energy. The desired echo signals aretherefore horizontally polarized. At the beginning of the next pulserepetition period, a different standing-wave is caused to beestablished; and the second-time-around echo signals (due to targetsbeyond the range of interest) are no longer accepted by the antenna.(Target signals received from targets at ranges greater than thatrepresented by the interval of two successive pulse repetition periodsare presumed to be so attenuated in signal strength as to benegligible.)

Thus, the present invention may be employed to obviatesecond-time-around signals.

Since, because of the previously-discussed theory of reciprocity, thetransmission radiation-pattern is similar to the reception-pattern, theterm beam-pattern will now be used to include both the transmission andreception patterns.

As previously indicated, it is frequently desirable to control thebeam-pattern in which the emergent energy is radiated and received; andFIGURE shows one way of producing different beam-patterns, using thepresent inventive concept. In FIGURE 5, antenna 90 has a first set ofslots 92-shown to be transverse, but which may be either transverse orlongitudinalextending substantially from one end of the antenna to theother. When a suitable standing-wave pattern is established, by meanssuch as the shorting-plate 94 as described above, the first set of slots92 will emit energy that is polarized in a particular manner.

Due to the large longitudinal spatial distribution of the first set ofslots 92 (e.g. the longitudinal distance between the upper and lowerslots or extremities of the array of slots 92), when this set of slotsis emitting energy, the antenna will act as a large aperture antenna;and will produce a corresponding narrow beam of polarized energy asindicated by the narrow beam-pattern 96 of FIG- URE 6, in a planeparallel to the longitudinal axis of antenna 90 (FIGURE 5).

Antenna 90 of FIGURE 5 also contains a second set of slots 100, whichare oriented perpendicularly to the slots 92 of the first set; slots 100being relatively few in number (e.g., the longitudinal array of slots100 being shorter than the longitudinal array of slots 92). Inaccordance with the previous explanation, when a suitable standing-wavepattern is established, this second set of slots 100 will emit energythat is polarized perpendicularly to the energy from the first set ofslots.

Due to the smaller spatial distribution of the second set of slots 100(e.g., the longitudinal distance between the upper and lower slots orextremities of the array of slots 100), when the second set of slots isemitting energy, the antenna will act as a small aperture antenna; andwill produce a corresponding wide beam, (as indicated by referencecharacter 102 of FIGURE 6) in a plane parallel to the longitudinal axisof antenna 90 (FIGURE 5).

It may therefore be seen that, when suitably energized, the antenna 90of FIGURE 5 can produce either a wide or a narrow beam of energy (in aplane parallel to the longitudinal axis of antenna 90), the polarizationof the particular pattern depending upon the orientation of theenergized slots.

It was indicated above, that antenna 90 of FIGURE 5 needs two differenttypes of standing-wave patterns, in order to energize the two separatesets of slots. This result may be produced by using insertableshorting-plates as described previously; but in order to switch rapidlyfrom one radiation-pattern to the other, a different method may be used,as follows.

In FIGURE 5, the shorting plate 94 reflects the incoming energy toestablish a first standing-wave pattern that energizes the first set ofslots. When it is desired to adjust the standing-wave pattern so as toenergize the second set of slots, a set of electrically-conductiveshortingpins 104 are inserted into the waveguide; these effectivelyforming a shorting-plate. Because of its location, the effectiveshorting-plate produced by the shorting-pins 104 now establishes adifferent standing-wave pattern, which energizes the second set ofslots.

It may thus be seen that by inserting or withdrawing shorting-pins 104,either of two standing-wave patterns may be produced; each standing-wavepattern being capable of exciting a different set of slots. Since theshortingpins 104 can be rapidly inserted or withdrawn by actuation meanssuch as a magnet 106, the antenna is able to produce a wide or a narrowbeam of the desired polarization; and to quickly switch from one beam tothe other. Accordingly, antenna 90 of FIGURE 5 is adapted for providinga selected combination of beamwidth and polarization.

It is evident that even the mechanical shorting-pin arrangement ofFIGURE 5 has a limitation on the rapidity with which the pins can beinserted and withdrawn. This limitation is overcome in the arrangementof FIGURE 7, which also shows a different type of slot arrangement.

Here, antenna 110, instead of having longitudinal and transverse slots,has a set shown in solid lines, of pairs o oppositely inclined slots112A, 114A; 112B, 114B; 112C 114C; etc. Each slot of each pair couplesto a standingwave; and each pair of inclined slots produces longitud'nally-polarized emergent energy.

Antenna 110 also has a second set, shown in dotted lines, of pairs ofoppositely inclined slots 116A, 118A; 116B, 118B; 116C, 118C; etc. Eachslot of each pair couples to a standing-Wave; and each pair of inclinedslots produces longitudinally-polarized emergent energy.

The first set of slots 112-114 has a large spatial coverage(corresponding to the array of slots 92 in FIGURE 5); while the secondset of slots 116, 118 has a small spatial coverage (corresponding to thearray of slots in FIGURE 5). Thus, when the first set of slots-havingthe large spatial coverage-is energized by a suitable standing-wave, theantenna acts like a large antenna, and produces a narrow beam. However,when the second set of slotshaving a small spatial coverageis energizedby a different standing-wave, the antenna acts like a small antenna, andproduces a wide beam.

Thus, antenna of FIGURE 7 is capable of producing both the narrow andbroad beams 96 and 102 of FIG- URE 6. It should be noted however, thatin the case of antenna 110, both beams have the same linearpolarization. Accordingly, antenna 110 of FIGURE 7 is adapted forproviding a selected combination of beamwidth and polarization.

FIGURE 7 also shows another way of producing different standing-waves.One standing-wave is produced by a sorting-plate 119, as previouslydescribed. However, a plurality of electronically controlled waveguideswitches, such as varactor-diodes 120, takes the place of thepreviously-described shorting-pins. These varactor-diodes have thecharacteristic that they can be activated (by means of passing a directcurrent therethrough) to serve as an effective microwave shorting-plate;or they can be deactivated (by adjusting or reducing the currenttherethrough) to serve as a matched impedancewhereby the antenna acts asthough the varactor-diodes were not in the antenna at all.

Thus, when the varactor-diodes are activated, they have the effect ofproducing a standing-wave that energizes one set of inclined slots;whereas when the varactordiodes are matched, the physical shorting-plate119 produces another standing-Wave that energizes the other set ofinclined slots.

In FIGURE 7, the varactor-diodes, instead of being located near the endof the antenna, are instead located onehalf wavelength beyond thefurthermost radiating aperture; this location providing improvedoperation of the smaller-number set of inclined slots.

It will be realized that varactor-diodes may be used in the antennaspreviously discussed. Referring back to FIG- URE 3, for example,varactor-diodes can replace the illus trated shorting-plates; and, infact, a plurality of suitablylocated varactor-diodes may be used toproduce effective shorting-plates at a plurality of locationsintermediate to the illustrated shorting-plates. By suitably activatingthe varactor-diodes, a plurality of different standing-waves can beestablished; and the emergent energy can therefore be polarized in awide variety of polarizations.

In addition, a set of varactors may be activated to act as continuouslyvariable phase shifter; whereupon the polarization of the emergentenergy will vary continuously through a given range of polarizations.

The previous discussion has shown how the disclosed antenna can providea beam having a selected combination of beamwidth and polarization.Under some conditions, it is desirable to have two similar but notidentical beams; one of the beams to be used for transmitting radarenergy, while the other beam is used for receiving echo signals. FIGURE8 schematically shows an arrangement for achieving this result.

Referring to FIGURE 8, there is illustrated an antenna 140 comprising asymmetrical T-shaped antenna structure; the energy being introduced intothe stem-portion 142 of the T, and the horizontal-bar portion 144 of theT having two sets of paired inclined slots of the type previouslydescribed. One set of inclined slots is shown in solid lines, while theother set of inclined slots is shown in dotted lines.

When energy is applied through stem-portion 142 to antenna 140, thepassive or physical shorting-plates 146 at the end of the horizontal barof the T establish a continuous standing-wave between them; thestanding-wave exciting the set of inclined slots shown in dotted outlinein accordance with the previously-discussed principles. Because of thelarge spatial extent covered by the array of dotted-line slots, theantenna acts as a large antenna that has a narrow-beam transmissionpattern.

When it is desired to receive echo signals, both varactordiodes 148 maybe activated (by means well understood in the art) whereby they act aseffective shorting-plates as previously described; the effectiveshorting-plates establishing a continuous standing-wave that activatesthe second set of inclined slots shown in the solid-line slots. Theantenna again acts as a large antenna that has a narrow-beam receptionpattern.

In order to establish slightly different transmission and receptionpatterns, each set of slots may have a slightly different arrangementthan the other. For example, the slots of one set may be different insize, orientation, or offset, compared with the slots of the other set;so that one set of slots produces a transmission-pattern that is similarbut slightly different from the reception-pattern produced by the otherset of slots.

Monopulse radar systems use a concept known as sum and differencesignals; corresponding to the even and odd distributions, respectively,of a target signal, as described, for example, in Introduction toMonopulse, by Rhoades (published by McGraw-I-Iill, 1959). Theapplication of such concept employs two reception antenna patterns whichare severally combined as shown in FIGURE 9, to provide the single long,narrow sum beam 130, shown in solid line and representing the sum of thetwo reception patterns, the two smaller lobes 132 shown by the dottedlines representing the difference between the two reception patterns.

The above-discussed theory of reciprocity also applies to an antennathat directly produces the sum and difference patterns of FIGURE 9. Thismeans that where, by means of the invention, an antenna transmits anarrow sum beam, its reception-beam will also be narrow; that is, theantenna will be more sensitive to echo signals originating dead-ahead(corresponding to the boresight axis or axis of symmetry of adirectional antenna), and will be lesssensitive to echo signalsoriginating off to one side of the boresight axis.

Similarly if the antenna, by means of the invention, is caused totransmit a two-lobed difference beam, the reception response thereofwill be sensitive to echo signals originating in such difference beam.

An antenna using the disclosed inventive concept can produce these sumand difference beam patterns; and the symbolic antenna representation ofFIGURE 10 shows how this can be done. Here, antenna is similar to thosepreviously discussed, in that it has two sets of inclined slots; one setof slots being shown in solid lines, while the second set of slots isshown in dotted lines.

The antenna 150 of FIGURE 10 produces a singlelobed narrow beam asfollows. Varactor-diode 152 is activated to produce an effectiveshorting-plate, so that the antenna is symmetrical. Energy applied tothe antenna coacts with the effective shorting-plate produced byvaractor-diode 152 and the physical shorting-plate 154, to produce acontinuous standing-wave between them. The standing-wave causes thesolid-line slots to be energized, so that each half of the antennaproduces a signal that is in-phase with the signal from the other halfof the antenna. In this way the antenna produces a single-lobed patternas described in connection with the previous illustration.

In accordance with the theory of reciprocity, incomingecho signals wouldenter the slots, and would establish a similar standing-wave. Thisstanding-wave would be coupled to the stem-portion of the antenna; andwould rovide sum-signals to utilizing equipment.

If it were desired to transmit the two-lobed difference beam,varactor-diode 152 would be de-activated, or matched (i.e., an appliedcurrent to the diode being controlled or adjusted, as required); anddiode 155 would be activated to produce an effective shorting-plate.Under these conditions, the antenna would no longer be symmetrical. Theleft half of antenna 150 establishes a standing-wave that would radiateenergy of a given polarization from the dotted-line inclined slots inthe left half of the antenna.

However, the right half of the antenna of FIGURE 10 would act in asomewhat dilferent manner. It will be seen that the physicalshorting-plate 156 is now three-quarters of a wavelength from theclosest dotted-line slot. This arrangement would establish astanding-wave that would cause the dotted-line slots of the right halfof the antenna to radiate energy that is out-of-phase (anti-phase)compared with the energy that would be radiated by the dotted-line slotsof the left half of the antenna. Hence, the mutually anti-phase energyradiated from the two halves of antenna 150 would co-act to produce thetwolobed ditference pattern 132 of FIGURE 9.

In accordance with the theory of reciprocity, incoming echo signalsreceived by the antenna of FIGURE 10 would enter the slots, and wouldestablish two similar anti-phase standing-waves. These anti-phasestanding-' 1 ll ence manner-the received echo signals appearing at thestem portion in a manner determined by the instantaneous standing-wave,as established by the states of the varactordiodes.

In a preferred application of such arrangement, the varactor diodeswould be gated in synchronism with the system trigger of a pulsed radarto provide a sum transmission pattern, and then alternately-gated insuch combination, as to provide sampled sum and difference signals foramplification by a single channel amplifier, the output of the amplifierbeing switched between two output terminals (by electronic gating meanswell-known in the art) in synchronism with the gating of the varactorsin order to separate the sum and difierence signals into two several anddistinct monopulse receiver outputs. In this way, monopulse receivergain tracking errors are avoided due to the time-shared use of a singlecommon amplifier for the sum and difierence receiver signals. Thearrangement of FIGURE 11 shows a time-duplexing arrangement forseverally processing sum and difference antenna pattern signals at theantenna.

The antenna 160 of FIGURE 11.is similar to that of FIGURE 10, in thatthe antenna inherently has sum and difference patterns that arecontrolled by the state of varactor-diodes 152, as previously explained.In FIG- URE 11, however, a four-port microwave hybrid T or magic tee 162is used, instead of the simple T of FIG- URES 9 and 10; the magic teehaving two ports or openings 171 and 172 thereof coupled to the antenna,a third port 163 symmetrically cooperates with the first two ports 171and 172 as to represent a sum port while a fourth port 164 issymmetrically cooperated with the first two as to represent a differenceport.

The construction and arrangement of magic tees is well known in the art,being described for example at' page 572 in volume 12 of the RadiationLaboratory Series, Microwave Antenna Theory and Design, by Silver(published by McGraw-Hill, 1949).

Where the varactor diodes 152 are switched to alternate states arespective one of the two slotted arrays are coupled to the waveguidesection 160, as previously explained. Hence, the beam pattern of theantenna of FIG- URE 11 is alternately a sum and difierence beam pattern.

Where varactors 152 are switched to a first state corresponding to a sumpattern during the application of a microwave energy pulse to sum port163 of T 162, then a sum pattern of energy is radiated from the antennaof FIGURE 11. If the varactors 152 are maintained in said first stateduring the receiving interval subsequent to the occurrence of thetransmitted pulse, then the sum receiving pattern provided by each ofthe left and right-hand sections of the slotted waveguide element ofFIGURE 11, as applied to the corresponding first and second port ofmagic tee 164, will be ditierentially combined at the output of thedifference or receiving port 164 to provide a mononpulse ditferencesignal.

If, however, the varactors 152 in FIGURE 11 are switched to a secondstate corresponding to a difierence antenna pattern, during thereceiving interval, then the difierence pattern provided by each of theleft and righthand sections of the slotted waveguide elements of FIG-URE 11 (as applied to the corresponding ports of magic tee 162) Will bedifferentially combined at the output of receiving port 164 to provide amonopulse sum signal.

Where the state of varactors 152 is cyclically alternated during areceiving interval of an associated radar system (not shown), then theantenna of FIGURE 11 may be employed as a time-shared monopulsereceiving antenna for use in cooperation with a single channelmononpulse receiver. Further, where the varactors are maintained in thefirst state during the pulsing interval of a radar transmitter (notshown) in response to the system trigger thereof and then cyclicallyalternated between the first and second states during the receivinginterval of the radar system, the antenna may be employed as a dup- 12lexed, time-shared antenna in a pulsed radar system having a time-sharedsingle channel monopulse receiver.

While the foregoing explanation has been given in terms of antennascomprising rectangular waveguides that have standing-waves producedtherein, the present inventive concept is also applicable to circular,elliptical, or other cross-sectional waveguides that have standingwavesproduced therein. For example, FIGURES 12 and 13 show a circular and anelliptical waveguide respectively, these waveguides having slot-pairssimilar to those of a previous illustration. In the structures ofFIGURES 12 and 13, the slot-pairs are spaced in accordance with theprevious explanations; and suitably-positioned shortingplates,varactor-diodes, or the like, produce desired standing-waves that causeenergy to escape through the slots.

Because of the difficulty of illustrating the complex standing-Wavesthat exist in these types of waveguides no detailed explanation will begiven; but use of the abovedescribed principles and types of slots willconvert waveguides of other than rectangular cross sections intoantennas capable of producing various types of polarization and beampatterns.

Accordingly, it is to be appreciated that an improved antenna has beendescribed, comprising means for providing selected combinations ofpolarization and beam patterns.

Although the invention has been illustrated and described in detail, itis to be clearly understood that the same is by way of illustration andexample only, and is not to be taken by way of limitation; the spiritand scope of this invention being limited only by the terms of theappended claims.

I claim:

1. An antenna comprising an apertured waveguide having two sets ofperpendicularly-oriented apertures, the apertures of the first setcoacting with the apertures of the second set to form aperture-pairs;means for producing a standing-wave in said waveguide, and causingenergy to escape from said aperture-pairs in an ellipticallypolarizedmanner; and

voltage-sensitive means for selectively changing said standing-wave toeffect a selected ellipticity of said escaping energy.

2. An antenna comprising an apertured waveguide having a first set ofinclined slots, and a second set of inclined slots;

switchable waveguide impedance means for establishing a standing-waveoperative to couple to an alternate one of said first and second sets ofinclined slots for causing an alternate one of said sets of inclinedslots to be associated with a corresponding one of a first and secondbeam-pattern.

3. An antenna comprising an apertured Waveguide having a first set ofinclined slots, a second set of inclined slots, and a third set ofinclined slots;

first means for establishing a standing-wave capable of coupling to saidfirst set of inclined slots, and causing said first set of inclinedslots to be associated with a beam of a first beam-pattern; second meansfor establishing a standing-wave capable of coupling to said second setof inclined slots, and causing said second set of inclined slots to beassociated with a beam of a second beam-pattern; and

third means for establishing a standing-Wave capable of coupling to saidthird set of inclined slots, and causing said third set of inclinedslots to be associated with a beam of a third beam-pattern.

4. An antenna comprising an apertured Waveguide having a first set ofinclined slots, a second set of inclined slots, and a third set ofinclined slots;

first means for establishing a stand-wave capable of coupling to saidfirst set of inclined slots, and causing said first set of inclinedslots to be associated with a beam of a first beam-pattern;

second means for establishing a standing-wave capable of coupling tosaid second set of inclined slots, and causing said second set ofinclined slots to be associated with a beam of a second beam-pattern;and

third means for establishing a stand-Wave capable of coupling to saidthird set of inclined slots, and causing said third set of inclinedslots to be associated with a beam of a third beam-pattern;

a magic-tee; and

means for coupling one port of said magic-tee with the set of slotsassociated with one of said beam patterns, and for coupling another portof said magictee with the sets of slots associated with the other twobeam-patterns.

5. In a time-shared, single channel microwave monopulse receivingantenna the combination comprising A microwave feed having a first andsecond slotted array,

Said first slotted array being responsive to an even distribution ofreceived energy corresponding to a monopulse sum signal;

Said second slotted array being responsive to an odd distribution ofreceived energy corresponding to a monopulse difierence signal;

Voltage-sensitive impedance coupling means adapted to be connected to asource of a switching signal for alternately coupling said first andsecond arrays to said microwave feed.

6. In a duplexing microwave antenna for transmitting and receiving radarenergy the combination comprising A four-port microwave hybrid tee,

A first and second port of said tee adapted to be connected to a radartransmitter and receiver respectively;

microwave-Wave feed means having A first and second slotted arrayadapted for generating a monopulse sum and difierence a11- tenna patternrespectively, said microwave feed means comprising a first and secondwaveguide section coupled to a third and fourth port respectively ofsaid hybrid tee;

variable microwave impedance means for alternatively coupling each ofsaid arrays to said microwave feed, whereby said antenna is enabled toprovide alternatively .a monopulse sum pattern in response totransmitted energy applied to said first port of said hybrid tee and amonopulse sum pattern in response to a received energy output occurringat said second port of said hybrid tee.

7. A cross-polarized linear array microwave energy antenna including,

a rectangular waveguide including means for applying microwave energythereto,

means for providing a standing wave pattern within said waveguide havingthe maximum transverse current amplitudes occurring at position ofminimum longitudinal current amplitudes,

14 at least one series slot in said waveguide and positionedsubstantially /2 guide wavelength points of said standing wave pattern,developed by said means for providing, at least one shunt slot in saidwaveguide and positioned substantially at /2 guide wavelength points ofsaid standing wave pattern, developed by said means for providing, and

means for selectively shifting the standing wave pattern by an amountequal to an odd number of quarter of guide wavelengths of the energy insaid waveguide.

8. A microwave antenna providing selected combinations of polarizationand beamwidth of an emergent beam and having a microwave feed andcomprising At least two slotted array-s fed at one extremity thereof bysaid feed; and

Voltage-sensitive microwave impedance means coupling said arrays to saidfeed, and comprising passive microwave shorting means beyond a secondextremity of said arrays and spaced apart therefrom and voltagesensitive microwave phase-shifit means interposed between said secondextremity of said arrays and said passive shorting means.

9. A linear array microwave energy antenna including, a waveguideincluding means for applying microwave energy thereto; means forproviding a standing wave pattern within said waveguide having themaximum transverse current amplitudes occurring at positions of minimumlongitudinal current amplitudes;

at least one series slot in said waveguide and positioned substantiallyat /2 guide wavelength points of said standing wave pattern, developedby said means for providing;

at least one shunt slot in said waveguide and positioned substantiallyat /2 guide wavelength points of said standing wave pattern, developedby said means for providing; and

means for selectively shifting the standing Wave pattern by an amountequal to an odd number of quarter of guide wave-lengths of the energy insaid waveguide.

References Cited UNITED STATES PATENTS 2,479,209 8/ 1949 Chu 3437712,679,590 5/ 1954 Riblet 343771 2,764,756 9/ 1956 Zaleski 3437 7 12,771,605 11/1956 Kirkman 343-771 2,982,960 5/196 1 Shanks 34*376 76,005,984 10/1961 Winder et M. i 3437'71 FOREIGN PATENTS 760,388 10/1956 Great Britain.

HER-MAN KARL SAALBACH, Primary Examiner.

-E-LI LIEBERMAN, Examiner.

M. NUSSBAUM, Assistant Examiner.

2. AN ANTENNA COMPRISING AN APERTURED WAVEGUIDE HAVING A FIRST SET OFINCLINED SLOTS, AND A SECOND SET OF INCLINED SLOTS; SWITCHABLE WAVEGUIDEIMPEDANCE MEANS FOR ESTABLISHING A STANDING-WAVE OPERATIVE TO COUPLE TOAN ALTERNATE ONE OF SAID FIRST AND SECOND SETS OF INCLINED SLOTS FORCAUSING AN ALTERNATE ONE OF SAID SETS OF INCLINED SLOTS TO BE ASSOCIATEDWITH A CORRESPONDING ONE OF A FIRST AND SECOND BEAM-PATTERN.